Method of forming oxynitride film

ABSTRACT

A method of forming a nitrogen-incorporated silicon or metal oxide film, includes (i) depositing by a plasma a silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (ii) nitriding by a plasma the silicon or metal oxide film using a nitriding gas without using any precursor, said plasma having a second plasma density which is higher than the first plasma density.

BACKGROUND Field of the Invention

The present invention relates generally to a method of forming an oxynitride film in the field of semiconductor fabrication processes.

Related Art

There is a demand for high quality SiO films deposited by plasma-enhanced atomic layer deposition (PEALD), having properties such as low wet etch rates and high withstand voltages. Conventionally, a common method for depositing such films is using high RF power and long duration of RF power application. However, even by using such method, the wet etch rate of films is not lower than approximately 2.0 relative to the wet etch rate of thermal oxide film, and the breakdown voltage (hereinafter “Vbd”) of films is not higher than approximately 10 MV/cm. Further, under plasma conditions of such method, oxidation of underlying films or film-deposited substrate by a plasma become a more apparent problem. That is, conventionally, in order to form SiO films having low wet etch rates and good withstand voltages, RF power for generating a plasma is increased, and/or high temperatures such as those higher than 1,000° C. are employed (high temperature deposition of thermal oxide film can provide better film quality). However, as compared with PEALD, film thickness control in the order of angstrom is difficult, and also there is a limitation imposed on process temperature due to thermal degradation of underlying film. Accordingly, desired is depositing a film at a low temperature such as 500° C. or lower while providing good film quality. As another approach, a method wherein SiON films are formed by PEALD by alternately depositing a SiO film and a SiN film has been reported. However, since switching two processes (one for depositing a SiO film and the other for depositing a SiN film) is required, this approach has inherently a problem of complexity of process.

Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.

SUMMARY

According to embodiments of the present invention, a method of forming a film having lower wet etch rates than those of conventional SiO films and having good withstand voltages is provided.

In this disclosure, a SiO film is a film characterized or recognized as a silicon oxide film which may include other elements such as nitrogen, carbon, hydrogen, etc. and unavoidable impurities to the extent that such elements do not materially change the characteristics of the silicon oxide film, and a SiON film is a film characterized or recognized as a silicon oxynitride film, not as a silicon oxide film nor a silicon nitride film, and which may include other elements such as carbon, hydrogen, etc. and unavoidable impurities to the extent that such elements do not materially change the characteristics of the silicon oxynitride film; and similarly, a SiN is a film characterized or recognized as a silicon nitride film, and which may include other elements such as oxygen, carbon, hydrogen, etc. and unavoidable impurities to the extent that such elements do not materially change the characteristics of the silicon nitride film, wherein the film names, such as SiO film, SiON film, and SiN film, are abbreviations indicating merely the film types (indicated simply by primary constituent elements) in a non-stoichiometric manner unless described otherwise.

In order to solve at least one of the problems in the conventional approaches, the inventors have developed technology which can achieve low wet etch rates of SiO films by incorporating nitrogen into SiO films which are deposited by PEALD in exemplary embodiments. In this disclosure, in exemplary embodiments, the term “incorporating nitrogen” refers to introducing nitrogen into the molecular structures constituted by Si—O bonds in a SiO film, by replacing some Si—O bonds with Si—N bonds via a substitution reaction, thereby generating a SiON film. In alternative embodiments, oxygen is incorporated into a SiN film, and the term “incorporating oxygen” refers to introducing oxygen into the molecular structures constituted by Si—N bonds in a SiN film, by replacing some Si—N bonds with Si—O bonds via a substitution reaction, thereby generating a SiNO film.

In some embodiments, by using lower RF power than conventionally used RF power, e.g., less than 300 W and/or using lower process temperature than conventionally used process temperatures, e.g., lower than 500° C., a film is deposited so as to suppress oxidation of an underlying film, and by conducting certain treatment prior to, during, and/or subsequent to deposition of the film, a film having high film quality can be formed. In this disclosure, unless otherwise specified, any indicated RF power is that for a 300-mm wafer and can be converted to W/cm² (wattage per unit area of a wafer) which can apply to a wafer having a different diameter such as 200 mm or 450 mm.

In some embodiments, a film formation method comprises a step of depositing a SiO film comprised of deposition cycles using an oxygen source, e.g., BDEAS (bis(diethylamino)silane) as a single precursor or a single combination of precursors, and a step of a plasma treatment for nitriding the SiO film, wherein high film quality in the resultant film can be achieved by manipulating the treatment conditions and treatment sequence. Since only the single precursor or single combination of precursors is used to form a SiON film, without switching a SiO film formation sequence and a SiN film formation sequence, a SiON film can be produced with high productivity and high stability. Further, since the apparatus uses only one bottle for storing the precursor (when the single precursor is used), the apparatus can be provided inexpensively and can be operated with high operation rates.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a dielectric film pertinent to an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between wet etch rate (“WER Tox ratio”) of a silicon oxide film relative to that of a thermal oxide film, and RF power (high-frequency) (“HRF”) used for depositing the silicon oxide film.

FIG. 3 shows a STEM (Scanning Transmission Electron Microscope) photograph of cross-sectional views showing a silicon oxide film as deposited in trenches (“As depo”) and showing the silicon oxide film after wet etching enclosed in a square (“After Wet etching”) which is superimposed on the photograph.

FIG. 4 shows a graph indicated by -♦- (“Depo only”) showing the relationship between wet etch rate (“WERR [/TOX]”) of a silicon oxide film relative to that of a thermal oxide film, and the number of wet etching cycles applied to the silicon oxide film (“Wet etching cycles”), and a graph indicated by -▴- (“Treated”) showing the relationship between wet etch rate (“WERR [/TOX]”) of a nitrogen-incorporated silicon oxide film relative to that of a thermal oxide film, and the number of wet etching cycles applied to the silicon oxide film (“Wet etching cycles”) according to an embodiment of the present invention.

FIG. 5 shows a STEM photograph of cross-sectional views showing a nitrogen-incorporated silicon oxide film as deposited in trenches (“As depo”) and showing the nitrogen-incorporated silicon oxide film after wet etching enclosed in a square (“After Wet etching”) which is superimposed on the photograph according to an embodiment of the present invention.

FIG. 6 shows an enlarged partial view of a STEM photograph similar to that in FIG. 5, showing a layer structure of the nitrogen-incorporated silicon oxide film as deposited (“As depo”).

FIG. 7 illustrates a schematic process sequence of formation of a nitrogen-incorporated silicon oxide film according to an embodiment, wherein the width of each column does not necessarily represent the actual time length, and a raised level of the line in each row represents an ON-state whereas a bottom level of the line in each row represents an OFF-state.

FIG. 8 shows a schematic process sequence of deposition of a silicon oxide film in combination with a schematic process sequence of nitridation of the silicon oxide film according to an embodiment of the present invention, wherein a cell in gray represents an ON state (darker gray represents higher intensity) whereas a cell in white represents an OFF state, and the width of each column does not represent duration of each process.

FIG. 9 is a flowchart illustrating steps of formation of a nitrogen-incorporated silicon oxide film having a desired layer structure according to an embodiment of the present invention.

FIG. 10 is a graph showing the relationship between RI of a nitrogen-incorporated silicon oxide film (“R.I.@633nm”) and RF power for depositing a silicon oxide film (“Depo RF power”) according to an embodiment of the present invention.

FIG. 11 is a Fourier Transform Infrared (FT-IR) spectrum of a nitrogen-incorporated silicon oxide film (“a: Treated”) according to an embodiment of the present invention and that of a silicon oxide film (“b: Depo only”) according to a comparative example.

FIG. 12 is a Fourier Transform Infrared (FT-IR) spectrum of a nitrogen-incorporated silicon oxide film (“a: Treated”) according to another embodiment of the present invention and that of a silicon oxide film (“b: Depo only”) according to another comparative example.

FIG. 13 is analytical results of X-ray photoelectron spectroscopy (XPS) of a nitrogen-incorporated silicon oxide film (“Treated”) in a depth direction of the film according to an embodiment of the present invention and those of a silicon oxide film (“Depo only”) in a depth direction of the film according to a comparative example.

FIG. 14 is a Fourier Transform Infrared (FT-IR) spectrum of a nitrogen-incorporated silicon oxide film (“a: Treated”) according to an embodiment of the present invention and that of a silicon oxide film (“b: Depo only”) according to a comparative example.

FIG. 15 is a graph showing the relationship between wet etch rate relative to thermal oxide film (“WERR [/TOX]”) and the number of wet etching cycles (“Wet etching cycles [times]”) of a nitrogen-incorporated silicon oxide film (“a: Treated”) according to an embodiment of the present invention and that of a silicon oxide film (“b: Depo only”) according to a comparative example.

FIG. 16 is a graph showing changes of refractive index at 633 nm (“RI@633 nm”) and changes of stress (“Stress [MPa]”) of a nitrogen-incorporated silicon oxide film over time (“Elapsed time [dd:hh:mm]”) according to an embodiment of the present invention.

FIG. 17 schematically illustrates layered structures constituted by a SiO layer and a SiON layer according to embodiments of the present invention, wherein a SiON layer constitutes an uppermost layer in (a), SiON layers and SiO layers are alternately stacked in a thickness direction in (b), and a SiON layer constitutes a bottom layer in (c).

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a precursor gas and an additive gas. The precursor gas and the additive gas are typically introduced as a mixed gas or separately to a reaction space. The precursor gas can be introduced with a carrier gas such as a noble gas. The additive gas may be comprised of, consist essentially of, or consist of a reactant gas and a dilution gas such as a noble gas. The reactant gas includes an oxidizing gas (e.g., oxygen-containing gas or oxygen source gas) and a nitriding gas (e.g., nitrogen-containing gas or nitrogen source gas). The reactant gas and the dilution gas may be introduced as a mixed gas or separately to the reaction space. A precursor may be comprised of two or more precursors, and a reactant gas may be comprised of two or more reactant gases. The precursor is a gas which can be chemisorbed on a substrate and typically contains a metalloid or metal element which constitutes a main structure of a matrix of a dielectric film, and the reactant gas for deposition is a gas which can react with the precursor chemisorbed on a substrate when the gas is excited to fix an atomic layer or monolayer on the substrate, or a gas which can react with a monolayer or stacked multiple monolayers to treat such layers. “Chemisorption” refers to chemical saturation adsorption. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a noble gas. In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers.

Further, in this disclosure, the article “a” or “an” refers to a species or a genus including multiple species unless specified otherwise. The terms “constituted by” and “having” refer independently to “typically or broadly comprising,” “comprising,” “consisting essentially of,” or “consisting of” in some embodiments. Also, in this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

Additionally, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments in various aspects. However, the present invention is not limited to the preferred embodiments.

Some embodiments are directed to a method of forming a nitrogen-incorporated silicon or metal oxide film, comprising steps of: (i) depositing by a plasma a silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (ii) nitriding (incorporating nitrogen into) by a plasma the silicon or metal oxide film using a nitriding gas without using any precursor (without depositing a film), said plasma having a second plasma density which is higher than the first plasma density. In some embodiments, the second plasma density is 1.1 times to 3 times higher (e.g., 1.3 times to 2 times) than the first plasma density.

In some embodiments, the nitrogen-incorporated silicon or metal oxide film refers to an integrated silicon or metal oxide film deposited using a same precursor, at least part of which is converted to silicon or metal oxynitride constituted by nitrogen-incorporated silicon or metal oxide which is expressed as SiON or MON, wherein the content of nitrogen is at least 1 atomic % but less than the content of oxygen, e.g., in a range of 2 atomic % to 30 atomic %, typically 5 atomic % to 20 atomic %, exemplarily approximately 10 atomic % (±3 atomic %). For example, a bottom layer (or an interface layer), a top layer, and/or at least one layer between the bottom and top layers are/is constituted by SiON or MON. In some embodiments, the entire silicon or metal oxide film is constituted by SiON or MON.

A plasma is a partially ionized gas with high free electron content (about 50%). Bombardment of a plasma can be represented by plasma density or kinetic energy of ions. The plasma density is also referred to as “electron density” or “ion saturation current density” and refers to the number of free electrons per unit volume. The plasma density in the reaction space can be measured using a Langmuir probe (e.g., LMP series) and can be determined using a probe method (e.g., “High accuracy plasma density measurement using hybrid Langmuir probe and microwave interferometer method,” Deline C, et al., Rev. Sci. Instrum. 2007 November; 78(11): 113504, the disclosure of which is incorporated by reference in its entirety). The plasma density can be modulated mainly by tuning the pressure and RF power (the lower the pressure and the higher the power, the higher the plasma density becomes). The plasma density can also be modulated by applying a DC bias voltage or an AC voltage with a lower frequency set for ions to follow (<1 MHz). If conditions for generating a plasma using a plasma-generating gas (wherein a precursor and a reactant are not taken into consideration), such as temperature and pressure and the type of plasma-generating gas, other than RF power, are substantially the same in step (i) and step (ii), the plasma density can be represented by RF power applied to the plasma-generating gas when determining which plasma has a higher plasma density than the other.

In some embodiments, the plasma is a capacitively coupled plasma (CCP). However, alternatively or additionally, a remote plasma or other plasmas such as inductively coupled plasma (ICP), electron cyclotron resonance plasma (ECP), and helicon wave plasma (HWP), which can generate, e.g., nitrogen radicals and nitrogen ions when a nitrogen source gas is exposed to the plasma, can be used. If the types of plasma such as above are different between the deposition step and the nitridation step, different reaction chambers may be used for the respective steps. An exemplary plasma-generating gas is a noble gas such as Ar, He, Kr, and any combination thereof.

As the precursor containing a silicon or metal (e.g., Mg, Al, Si, Ti, Ge, Zr, Ru, Hf, or Ta), any precursor which is capable of forming an oxide film can be used. For example, organic aminosilanes such as BDEAS (bisdiethylaminosilane), 3DMAS (tris(dimethylamino)silane), or the like, metal halides such as TiCl4, metal amides such as TDMAT (tetrakis(dimethylamino)titanium) and TDMAGe (tetrakis(dimethylamino)germane), or metalorganic compounds such as Ru(EtCp)2 (bis(ethylcyclopentadienyl)ruthenium) can be favorably used singly or in any combination of two or more of the foregoing. As each of a carrier gas and a dilution gas, Ar, He, or the like can be favorably used singly or in any combination of two or more of the foregoing. In some embodiments, the carrier gas is fed continuously to the reaction space throughout step (i) (and further throughout step (ii) in some embodiments). In some embodiments, in plasma-enhanced atomic layer deposition (PEALD), the duration of precursor feed cycle is in a range of 0.1 seconds to 2.0 seconds, e.g., 0.5 seconds to 1.0 seconds.

In some embodiments, the method further comprises, prior to step (i), (ii) nitriding by a plasma a surface of the substrate using a nitriding gas without using any precursor. In the above, if a substrate interface is constituted by silicon, the surface becomes silicon nitride, on which a SiO film is deposited in step (i), followed by step (ii) to nitride the SiO film, wherein a layer structure of Si/SiON/SiO/SiON can be formed. When a small amount of nitrogen is present on the substrate interface (light-degree interface nitridation), the electrical characteristics of the film may be improved, and further, adhesion of the SiO film may be improved.

In some embodiments, the timing and/or the repeating frequency of nitridation of step (ii) and step (ii) can be controlled in a manner performing nitridation on a substrate interface, at any given point during step (i) (i.e., at any given position in a thickness direction in the SiO film, e.g., between any monolayers of the SiO film), and/or on a top of the SiO film, and also, the quantity of nitrogen incorporated in the SiO film can be controlled, thereby tailoring a layer structure as desired, without complexity of process. In order to realize the above embodiments, in some embodiments, provided is a method of forming a nitrogen-incorporated silicon or metal oxide film by converting a silicon or metal oxide film to a silicon or metal oxynitride film at a desired location, comprising steps of: (a) designing a layer structure of a nitrogen-incorporated silicon or metal oxide film, which layer structure is composed of a layer A constituted by a silicon or metal oxide film and a layer B constituted by a silicon or metal oxynitride film; (b) according to the design, depositing, for the layer A, by a plasma the silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (c) according to the design, nitriding, for the layer B, by a plasma the silicon or metal oxide film using a nitriding gas without using any precursor in a manner converting the silicon or metal oxide film to the silicon or metal oxynitride film, said plasma having a second plasma density which is higher than the first plasma density. In some embodiments, the nitrogen-incorporated silicon or metal oxide film is constituted by multiple layers of the layer A and multiple layers of the layer B, alternately layered. In some embodiments, a ratio of a total thickness of the layer A to a total thickness of the layer B is 0/100 to 99/1 (e.g., 20/80, 30/70, 40/50, 50/50, and any ratios therebetween). In some embodiments, the thickness of the layer B (a layer of SiON) is 0.1 nm to 2 nm, exemplarily approximately 1 nm. Thus, for example, by conducting nitridation of step (c) after every deposition of SiO film having a thickness of approximately 1 nm in step (b), a layer structure entirely constituted by SiON can be formed. Alternatively, for example, by conducting nitridation of step (c) after every deposition of SiO film having a thickness of approximately 2 nm in step (b), a layer structure constituted by a stripe pattern composed of a SiO layer and a SiON layer without complexity of process. In some embodiments, step (c) is repeatedly conducted after every one to 100 cycles (e.g., two to 30 cycles) of PEALD in step (b), depending on the target layer structure.

In some embodiments, in step (i), the silicon or metal oxide film is deposited by PEALD. Accordingly, a conformal SiO film can be deposited in patterned recesses or steps of a substrate (e.g., trenches). A same structure can be referred to as a recess and also as a step where the structure is a recess with reference to a top surface whereas the structure is a step with reference to a bottom surface. In this disclosure, a trench, via hole, and any other recess are referred to as a “recess”. In some embodiments, the pattern is constituted by recesses or steps. In some embodiments, the recess has a width of 10 to 50 nm (typically 15 to 30 nm), a depth of 30 to 200 nm (typically 50 to 150 nm), and an aspect ratio of 3 to 20 (typically 3 to 10). In some embodiments, the oxide film has a conformality of 80% to 100% (typically about 90% or higher) wherein the “conformality” is determined by comparing film thickness deposited at some point (typically a midway point) on a sidewall or on a bottom of a recess to film thickness deposited on a flat surface just outside the recess.

In some embodiments, in PEALD, the oxidizing gas contains both oxygen and nitrogen, and exemplary oxidizing gas includes, but is not limited to, N₂O, NO, NH₃+O₂, and N₂+O₂. Alternatively, in some embodiments, in PEALD, the oxidizing gas contains oxygen without nitrogen, and exemplary oxidizing gas includes, but is not limited to, O₂, O₃, and the like.

In some embodiments, in PEALD, in step (i), the plasma is a capacitively coupled plasma (CCP) generated by applying RF power to electrodes, wherein a duration of RF power is 2.0 seconds or less (e.g., 0.1 seconds to 1.5 seconds, or 0.5 seconds to 1.2 seconds) in each cycle of PEALD and a power of RF power is 0.28 W per cm² of the substrate surface or less, i.e., 200 W or less (e.g., 35 W to 150 W, or 50 W to 100 W) for a 300-mm substrate, for example (the RF power (W/cm²) can be applied to a substrate other than a 300-mm substrate). By using relatively low RF power, a SiO film can be deposited without oxidizing an underlying film (e.g., the underlying SiON film previously nitrided in step (ii)), and additionally, the SiO film can be provided with a characteristic of relatively easily being nitrided (i.e., nitrogen is relatively easily incorporated into the SiO film), which may reside in, e.g., relatively low densification of the SiO film. For similar reasons, in some embodiments, a pulse of application of RF power has a duration of 2.0 seconds or less (e.g., 0.3 to 1.0 seconds, or 0.1 to 0.5 seconds). In some embodiments, RF power is of 200 kHz to 600 MHz, exemplarily 13.56 MHz. In some embodiments, inductively coupled plasma (ICP) or remote plasma (PR) can be used in place of CCP.

In some embodiments, the process temperature in step (ii) is in a range of 50° C. to 500° C., e.g., 300° C. to 400° C.; the process pressure in step (ii) is in a range of 200 Pa to 2000 Pa, e.g., 300 Pa to 400 Pa; the process temperature in step (i) is in a range of 50° C. to 500° C., e.g., 300° C. to 400° C.; and the process pressure in step (i) is in a range of 200 Pa to 2000 Pa, e.g., 300 Pa to 400 Pa.

In some embodiments, in step (i), the flow rate of the oxidizing gas is in a range of 500 sccm to 4,000 sccm, e.g., 1,000 sccm to 3,000 sccm; and the flow rate of the carrier gas is in a range of 500 sccm to 4,000 sccm, exemplarily about 2,000 sccm.

In some embodiments, in step (ii), the plasma is generated by applying RF power to the electrodes, wherein a power of RF power is 0.42 W per cm² of the substrate surface or higher, i.e., 300 W or higher (e.g., 300 W to 400 W) for a 300-mm substrate, for example, so that nitridation of the SiO film can be accomplished effectively. In some embodiments, RF power used in step (ii) is continuous, or alternatively, intermittently (pulsed). In some embodiments, RF power in step (ii) is of 200 kHz to 600 MHz, exemplarily 13.56 MHz, which is the same as in step (i).

In some embodiments, step (i) and step (ii) are conducted in a same reaction space or different reaction spaces to which an inert gas is supplied through steps (i) and (ii) so that step (i) and step (ii) can be performed continuously with high productivity and without unwanted particle contamination between step (i) and step (ii) or without unwanted oxidation when being exposed to air. The inert gas functions as a plasma-generating gas in steps (i) and (ii), and in step (ii), not only for nitridation of the oxide film, but for effective incorporation of nitrogen into the oxide film to convert the oxide film to a nitrogen-incorporated oxide film, use of the inert gas is effective to make nitrogen ions to more easily dissociate from the nitriding gas when it is exposed to a plasma of the inert gas. In some embodiments, in step (ii), a flow ratio of the nitriding gas to the inert gas is 1/99 or higher, e.g., 10/90 to 50/50. The flow ratio of the nitriding gas to the inert gas is a parameter controlling ease of ionization of nitrogen. In some embodiments, the nitriding gas is N₂, NH₃, or N₂+H₂. In some embodiments, the flow rate of the nitriding gas is in a range of 500 sccm to 4,000 sccm, e.g., 1,000 sccm to 3,000 sccm; and the flow rate of the inert gas (such as a noble gas) is in a range of 500 sccm to 4,000 sccm, exemplarily about 2,000 sccm.

In some embodiments, the process temperature in step (ii) is in a range of 50° C. to 500° C., e.g., 300° C. to 400° C.; the process pressure in step (ii) is in a range of 200 Pa to 2000 Pa, e.g., 300 Pa to 400 Pa; and the duration of step (ii) is in a range of 60 seconds to 600 seconds, e.g., 60 seconds to 180 seconds. In some embodiments, the process temperature and the process pressure are controlled in the same manner in steps (i) and (ii).

In some embodiments, in accordance with the same principle described above, an element other than nitrogen, such as B, C, Al, P, S, Ga, and As, can also be incorporated into a silicon or metal oxide film, which embodiments include a method of forming an element X-incorporated silicon or metal oxide film, comprising steps of: (i) depositing by a plasma a silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (ii) exciting an element X-containing gas by a plasma and incorporating the element X into the silicon or metal oxide film without using any precursor for deposition, said plasma having a second plasma density which is higher than the first plasma density. Since the element X can be incorporated in a manner similar to that for incorporating nitrogen, a skilled artisan in the art can readily provide conditions and/or structures not specified herein, in view of the present disclosure, as a matter of routine experimentation.

In another aspect of the present invention, some embodiments provide a method of forming an oxygen-incorporated silicon or metal nitride film, comprising steps of: (I) depositing by a plasma a silicon or metal nitride film on a substrate using a precursor containing a silicon or metal and a nitriding gas, said plasma having a first plasma density; and (II) oxidizing by a plasma the silicon or metal nitride film using an oxidizing gas without using any precursor, said plasma having a second plasma density which is lower than the first plasma density. Forming an oxygen-incorporated silicon or metal nitride film, in place of the nitrogen-incorporated silicon or metal oxide film described in this disclosure, can be performed in a manner substantially similar to the latter, and a skilled artisan in the art can readily provide conditions and/or structures for performing the former, in view of the present disclosure, as a matter of routine experimentation.

The present invention will be explained in detail with reference to embodiments shown in the drawings. However, the embodiments are not intended to limit the present invention.

FIG. 7 illustrates a schematic process sequence of formation of a nitrogen-incorporated silicon oxide film according to an embodiment, wherein the width of each column does not necessarily represent the actual time length, and a raised level of the line in each row represents an ON-state whereas a bottom level of the line in each row represents an OFF-state. In this embodiment, the oxide film deposition step and the nitriding step are performed in a same reaction chamber of a PEALD apparatus. The illustrated oxide film deposition step shows one cycle of PEALD which in principle corresponds to formation of a monolayer, and the cycle can be repeated until a desired film thickness is obtained before moving onto the nitriding step. In this embodiment, the carrier gas and the dilution gas are continuously fed to the reaction space through the oxide film deposition step and the nitriding step. The oxidizing gas is continuously fed to the reaction space only through step (i), whereas the nitrogen source gas is continuously fed to the reaction space only through step (ii), wherein during a transition period (a gas changing step) between the oxide film deposition step and the nitriding step, the flow of the oxidizing gas decreases to zero, whereas the flow of the nitrogen source gas increases from zero. The precursor is fed only in a pulse, followed by a pulse of RF power application, per cycle of deposition. In this embodiment, the carrier gas and/or the dilution gas function(s) also as a plasma-generating gas and a purge gas. In the nitriding step, RF power is applied without feeding any precursor.

In this embodiment, the oxide film deposition step and the nitriding step are performed in the same reaction chamber; however, these steps can be consecutively performed in different reaction chambers, and also, regardless of whether the same reaction chamber or different reaction chambers is/are used, the plasma-generating gas (e.g., noble gas) can be the same or different in the oxide film deposition step and the nitriding step. For example, in the oxide film deposition step, Ar is used whereas in the nitriding step, He is used, as the plasma-generating gas.

FIG. 8 show a schematic process sequence of deposition of a silicon oxide film in combination with a schematic process sequence of nitridation of the silicon oxide film according to an embodiment of the present invention, wherein a cell in gray represents an ON state (darker gray represents higher intensity) whereas a cell in white represents an OFF state, and the width of each column does not represent duration of each process. This schematic process sequence corresponds to that illustrated in FIG. 7. In this embodiment, the oxide film deposition step is a step of PEALD comprised of “Stable” (Stabilization) wherein the carrier gas/dilution gas and the oxidizing gas are fed to the reaction space for stabilizing the gas flow in the reaction space, “Feed” (0.1 to 1.0 seconds, preferably 0.2 to 0.5 seconds) wherein the precursor is fed to the reaction space while feeding the carrier gas/dilution gas and the oxidizing gas for adsorbing the precursor on a surface of a substrate, “Purge” (0.1 to 2.0 seconds, preferably 0.3 to 1.5 seconds) wherein the carrier gas/dilution gas and the oxidizing gas are continuously fed to the reaction space without feeding the precursor for removing non-adsorbed precursor and purging the reaction space, “Depo” (0.1 to 2.0 seconds, preferably 0.3 to 1.5 seconds) wherein RF power is applied to the reaction space while continuously feeding the carrier gas/dilution gas and the oxidizing gas without feeding the precursor for causing plasma reaction on the precursor-adsorbed surface of the substrate to form a monolayer, and “Purge” (0.05 to 1.0 seconds, preferably 0.1 to 0.5 seconds) wherein the carrier gas/dilution gas and the oxidizing gas are continuously fed to the reaction space without feeding the precursor for removing non-reacted components and by-products and purging the reaction space. The above constitutes one cycle of PEALD, and the cycle is conducted once or repeated several hundred times according to the target thickness for nitridation.

In the process sequence described above, the precursor is supplied in a pulse using the carrier gas which is continuously supplied. This can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 30. The carrier gas flows out from the bottle 30 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 30, and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B, the carrier gas flows through the gas line with valve a while bypassing the bottle 30. In the above, valves b, c, d, e, and f are closed.

After the oxide film deposition step is complete, a “Gas Flow” step begins to change the gas in the reaction space for nitridation, wherein the carrier gas/dilution gas are continuously fed to the reaction space whereas the oxidizing gas tapers off to zero while the nitrogen source gas begins to flow and gradually increase its flow in a manner substantially maintaining the pressure in the reaction space by balancing the decrease of the oxidizing gas and the increase of the nitriding gas. After “Gas Flow,” the nitriding step begins, which is comprised of “Stable” (Stabilization) wherein the carrier gas/dilution gas and the nitriding gas are fed to the reaction space for stabilizing the gas flow in the reaction space, “Treatment” wherein RF power is applied to the reaction space while continuously feeding the carrier gas/dilution gas and the nitriding gas without feeding any precursor for incorporating nitrogen into the oxide film from an exposed surface of the oxide film, and “Purge” wherein the carrier gas/dilution gas and the nitriding gas are continuously fed to the reaction space without feeding any precursor for removing non-reacted components and by-products and purging the reaction space. This step is conducted once after every one or several hundred cycles in the oxide film deposition step, and the oxide film deposition step and the nitriding step are conducted once or repeated a few dozen times according to the target layered structure and the target thickness of the resultant nitrogen-incorporated oxide film. For effectively suppressing oxidation of an underlying layer in the oxide film deposition step, and for effectively incorporating nitrogen into the oxide film, RF power (plasma density) in the nitriding step is higher than in the oxide film deposition step. RF power in the oxide film deposition step is lower than in the nitriding step to the extent that a wet etch rate of the resultant oxide film is approximately at least 2.5 times (e.g., 3 or 4 times) higher than that of thermal oxide film, i.e., RF power is so low that densification of the oxide film is incomplete.

FIG. 9 is a flowchart illustrating steps of formation of a nitrogen-incorporated silicon oxide film having a desired layer structure according to an embodiment of the present invention. In step S1, a target layer structure constituted by a silicon oxide (SiO) layer and a silicon oxynitride (SiON) layer is designed, wherein, for example, a bottom layer (or an interface layer), a top layer, and/or at least one layer between the bottom and top layers are/is constituted by SiON. In some embodiments, a stripe pattern composed of SiO layers and SiON layers alternately stacked in a thickness direction is formed. In some embodiments, the entire silicon oxide film is constituted by SiON. In step S1, layer structures such as those illustrated in FIG. 17 can be designed.

FIG. 17 schematically illustrates layered structures constituted by a SiO layer and a SiON layer according to embodiments of the present invention, wherein a SiON layer constitutes an uppermost layer in (a), SiON layers and SiO layers are alternately stacked in a thickness direction in (b), and a SiON layer constitutes a bottom layer in (c) (which may be referred to as an interface layer between a Si substrate and a nitrogen-incorporated silicon oxide film). In (b), each thickness of SiO and SiON layers can be adjusted by varying the number of SiO deposition cycles (step S3) per the treatment (step S4).

According to the target layer structure determined in step S1, if a bottom layer (or an interface layer) is to be constituted by SiON (when an underlying layer is a silicon substrate), step S2 is conducted, wherein before the oxide film deposition step (step S3), the nitriding step is conducted to nitride an underlying layer (the silicon substrate) to form an interface layer (a bottom layer) which becomes SiON as a result of oxidation when next step S3 is conducted. In step S3, the oxide film deposition step is conducted by PEALD wherein one to several hundred deposition cycles is conducted, and after step S3, the nitriding step is conducted (step S4). Step S4 is conducted once after step S3. Thereafter, according to the target layer structure determined in step S1, steps S3 and S4 are repeated in step S5. Steps S3 and S4 are conducted once or more times (e.g., a few dozen times).

In some embodiments, the deposition cycle of silicon oxide film is performed by PEALD under the conditions specified below:

A) An oxidizing gas contains nitrogen such as N₂O, NO, NH₃+O₂, and/or N₂+O₂. In some embodiments, an oxidizing gas contains oxygen without nitrogen such as O₂.

B) A carrier gas for a precursor is an inert gas such as Ar, He, Kr, and/or N_(2.)

C) A duration of plasma pulse for depositing a SiO layer is as short as 2.0 seconds or less.

D) RF power for depositing a SiO layer is as low as 200 W or less (for a 300-mm wafer).

In some embodiments, the nitridation of the silicon oxide film is conducted under the conditions specified below.

E) Nitridation is conducted before, during, and/or after the deposition step.

F) A gas containing nitrogen such as N₂, NH₃, and/or N₂+H₂ is used.

G) The nitrogen-containing gas is used by mixing it with Ar, He, or a combination of Ar and He.

H) A flow ratio of the nitrogen-containing gas to the mixed gas is 1/100 to 50/100 (1% to 50%).

I) RF power for nitridation is at least 300 W (for a 300-mm wafer).

J) No precursor is used.

A plasma for deposition may be generated in situ, for example, in an atmosphere of inert gas that flows continuously throughout the deposition cycle. In other embodiments the plasma may be generated remotely and provided to the reaction chamber. When a remote plasma is used in place of a direct plasma (e.g., CCP), a remote plasma unit may use 30 W to 8 kW of power to conduct the nitridation step.

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a gas-pulse PECVD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas (and noble gas) and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a dilution gas is introduced into the reaction chamber 3 through a gas line 23. Further, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere. In some embodiments, a remote plasma unit can be used for exciting a gas.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics, and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

In some embodiments, not only the locations of nitrogen incorporated in an oxide film, but also the incorporated quantity of nitrogen can be adjusted. The incorporated quantity of nitrogen can be adjusted by adjusting, e.g., the duration of the nitridation step, RF power applied to the reaction space, nitrogen concentration in the nitrogen source gas fed to the reaction space, and/or the process pressure in the reaction space during the nitridation step.

In another aspect of the invention, the technology can be applied to a silicon or metal nitride film and can incorporate oxygen into the silicon/metal nitride film. In some embodiments, the deposition cycle of silicon nitride film is performed by PEALD under the conditions specified below:

A) A gas containing nitrogen such as N₂, NH₃, and/or N₂+H₂ is used.

B) A carrier gas for a precursor is an inert gas such as Ar, He, Kr, and/or N_(2.)

C) RF power for depositing a SiN layer is at least 100 W (for a 300-mm wafer).

In some embodiments, the oxidation of the silicon nitride film is conducted under the conditions specified below.

D) Oxidation is conducted before, during, and/or after the deposition step.

E) An oxidizing gas contains nitrogen such as N₂O, NO, NH₃+O₂, and/or N₂+O₂. In some embodiments, an oxidizing gas contains oxygen without nitrogen such as O_(2.)

F) The oxidizing gas is used by mixing it with Ar, He, Kr, and/or N_(2.)

G) A flow ratio of the oxidizing gas to the mixed gas is 1/100 to 50/100 (1% to 50%).

H) A duration of plasma pulse for treating a SiN layer is as short as 2.0 second or less.

I) RF power for oxidation is 200 W or less (for a 300-mm wafer).

J) No precursor is used.

The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.

EXAMPLES Reference Example 1

SiO films were each deposited on a Si substrate (Φ300 mm) by PEALD under the conditions described below by varying RF power using the PEALD apparatus illustrated in FIGS. 1A and 1B based on the sequence illustrated in FIG. 7 as “Oxide Film Deposition Step” (without “Nitriding Step”).

Deposition Conditions: RF on time: 1.0 sec.; RF power (13.56 MHz): Varying, See FIG. 2; Pressure: 333 Pa; Susceptor temperature: 390° C.; Precursor: BDEAS; Carrier gas: He (2.15 slm); Dilution gas: He (1.05 slm); Oxidizing gas (reactant): N₂O (0.8 slm); Number of cycles: 600 (a thickness of the resultant film: 40 nm).

After taking each substrate out of the reaction chamber, the wet etch rate of each film was measured using a DHF (100:1) for 1 minutes. FIG. 2 is a graph showing the relationship between wet etch rate (“WER Tox ratio”) of the silicon oxide films relative to that of a thermal oxide film, and RF power (high-frequency) (“HRF”) used for depositing the silicon oxide film. As can be seen from FIG. 2, when RF power was 500 W or higher, the wet etch rate of the silicon oxide film relative to that of a thermal oxide film (“WERR”) was about 2.0, whereas when RF power was 200 W or less, the WERR was about 4.0 or higher. This shows that when RF power is 200 W or less, although oxidation of an underlying layer may be suppressed, WERR of the silicon oxide film becomes too high, i.e., the film quality becomes unsatisfactory.

Comparative Example 1

A SiO film was deposited on a Si substrate (Φ300 mm) having trenches having a depth of 100 nm, a width of 30 nm, and a pitch of 45 nm by PEALD in the same manner as in Reference Example 1, except that RF power was 100 W.

After taking each substrate out of the reaction chamber, the wet etching was conducted using a DHF (200:1) for 1 minutes. FIG. 3 shows a STEM (Scanning Transmission Electron Microscope) photograph of cross-sectional views showing the silicon oxide film as deposited in trenches (“As depo”) and showing the silicon oxide film after wet etching enclosed in a square (“After Wet etching”) which is superimposed on the photograph. As can be seen from FIG. 3, although when the silicon oxide film was deposited, its conformality was high (about 98%), after wet etching, portions of the film deposited on sidewalls of the trenches were almost totally removed. This means that even though portions of the film deposited on a top surface may have good WERR, portions of the film deposited on the sidewalls of the trenches have significantly high WERR. This is a second problem of conventional silicon oxide film (the first problem is oxidation of an underlying layer).

Example 1 and Comparative Example 2

In Example 1, a nitrogen-incorporated SiO film was formed on a Si substrate (Φ300 mm) by PEALD under the conditions indicated in Table 1 below using the PEALD apparatus illustrated in FIGS. 1A and 1B based on the sequence illustrated in FIGS. 8 and 9.

TABLE 1 (numbers are approximate) Parameters Deposition Substrate temperature 300° C. Cycle Pressure 400 Pa (PEALD) Precursor pulse 0.5 sec (BDEAS) Flow rate of oxidizing gas 0.8 slm (N₂O) (continuous) Flow rate of carrier gas 1.5 slm (He) (continuous) Flow rate of dilution gas 0.7 slm (He) (continuous) RF power (13.56 MHz) 100 W RF power pulse 1.5 sec The number of cycles 30 cycles Thickness of oxide film About 33 nm Nitridation Substrate temperature 300° C. Treatment Pressure 400 Pa Flow rate of nitrogen source 0.8 slm (N₂) gas (continuous) Total Flow rate of dilution 2.2 slm (Ar) gas (continuous) RF power (13.56 MHz) 500 W Duration of RF power application 300 sec The number of cycles (Depo + Nitridation) 20 cycles

As Comparative Example 2, a silicon oxide film was deposited on a Si substrate (Φ300 mm) by PEALD under the same conditions as in Example 1 except that no nitridation step was conducted.

After taking each substrate out of the reaction chamber, wet etching was conducted using a DHF (100:1) for 1 minute as one cycle at a total of 4 cycles. FIG. 4 shows a graph indicated by -♦- (“Depo only”) showing the relationship between wet etch rate (“WERR [/TOX]”) of the silicon oxide film (Comparative Example 2) relative to that of a thermal oxide film, and the number of wet etching cycles applied to the silicon oxide film (“Wet etching cycles”), and a graph indicated by -▴- (“Treated”) showing the relationship between wet etch rate (“WERR [/TOX]”) of the nitrogen-incorporated silicon oxide film (Example 1) relative to that of a thermal oxide film, and the number of wet etching cycles applied to the silicon oxide film (“Wet etching cycles”). As can be seen from FIG. 4, the nitrogen-incorporated silicon oxide film exhibits surprisingly improved wet etch resistance which is substantially equivalent to that of thermal oxide film, whereas the silicon oxide film without nitrogen incorporated exhibits high wet etch rates, i.e., poor wet etch resistance. Further, FIG. 4 shows that nitrogen was incorporated into the silicon oxide film not only on the surface but also through the surface and it reached a certain depth since even after four cycles of wet etching, WERR was still low.

Also, the nitrogen-incorporated silicon oxide film in Example 1 was subjected to other analyses. FIG. 16 is a graph showing changes of refractive index at 633 nm (“RI@633 nm”) and changes of stress (“Stress [MPa]”) of the nitrogen-incorporated silicon oxide film over time (“Elapsed time [dd:hh:mm]”). As shown in FIG. 16, RI and stress of the film did not change and was substantially stable for 2.5 days of exposure to the atmosphere air, and even after exposure to the atmosphere air for 7 days (not shown). The nitrogen-incorporated silicon oxide film obtained by this technology was a highly stable film.

Example 2

A nitrogen-incorporated silicon oxide film was formed on a Si substrate (Φ300 mm) having trenches having a depth of 110 nm, a width of 30 nm, and a pitch of 60 nm by PEALD in the same manner as in Example 1, except that the number of cycles (Depo+Nitridation) was 5 in place of 20 in Example 1.

After taking each substrate out of the reaction chamber, wet etching was conducted using a DHF (200:1) for 1 minutes. FIG. 5 shows a STEM photograph of cross-sectional views showing the nitrogen-incorporated silicon oxide film as deposited in trenches (“As depo”) and showing the nitrogen-incorporated silicon oxide film after wet etching enclosed in a square (“After Wet etching”) which is superimposed on the photograph. As can be seen from FIG. 5, when the nitrogen-incorporated silicon oxide film was deposited, its conformality was high (about 99%), and after wet etching, surprisingly, the high conformality was substantially maintained (about 97%), i.e., portions of the film deposited on sidewalls of the trenches were almost not removed. As compared with FIG. 3, the difference is remarkable. This means that nitridation can improve the film quality not only at portions of the film deposited on a top surface but also at portions of the film deposited on the sidewalls of the trenches.

FIG. 6 shows an enlarged partial view of a STEM photograph similar to that in FIG. 5, showing a layer structure of the nitrogen-incorporated silicon oxide film as deposited (“As depo”). It can be confirmed that there were five layers of silicon oxynitride which are indicated in darker gray.

Example 3

A nitrogen-incorporated silicon oxide film was formed by varying RF power on a Si substrate (Φ300 mm) by PEALD in a manner similar to that in Example 1 under the conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Parameters Deposition Substrate temperature 300° C. Cycle Pressure 400 Pa (PEALD) Precursor pulse 0.5 sec (BDEAS) Flow rate of oxidizing gas 0.8 slm (N₂O) (continuous) Flow rate of carrier gas 1.5 slm (He) (continuous) Flow rate of dilution gas 0.7 slm (He) (continuous) RF power (13.56 MHz) Varying, see FIG. 10 RF power pulse 1.5 sec The number of cycles 30 cycles Thickness of oxide film About 33 nm Nitridation Substrate temperature 300° C. Treatment Pressure 400 Pa Flow rate of nitrogen source 0.8 slm (N₂) gas (continuous) Flow rate of carrier gas 1.5 slm (He) (continuous) Total Flow rate of dilution 0.7 slm (He) gas (continuous) RF power (13.56 MHz) 500 W Duration of RF power application 300 sec The number of cycles (Depo + Nitridation) 20 cycles

After taking each substrate out of the reaction chamber, R.I. (refractive index) using light having a wavelength of 633 nm was measured. FIG. 10 is a graph showing the relationship between R.I. of the nitrogen-incorporated silicon oxide film (“R.I. @633 nm”) and RF power for depositing a silicon oxide film (“Depo RF power”). As can be seen from FIG. 10, when the nitrogen-incorporated silicon oxide film was deposited using RF power of 200 W or less, the R.I. of the resultant nitrogen-incorporated silicon oxide film was over 1.500, i.e., containing more Si—N bonds than did the nitrogen-incorporated silicon oxide film formed with RF power of 300 W or more, indicating that when RF power is 200 W or less for depositing a silicon oxide film, nitrogen can more smoothly be incorporated into the silicon oxide film.

Example 4 and Comparative Example 3

In Example 4, a nitrogen-incorporated silicon oxide film was formed on a Si substrate (Φ300 mm) by PEALD in the same manner as in Example 1. As Comparative Example 3, a silicon oxide film was deposited on a Si substrate (Φ300 mm) by PEALD under the same conditions as in Example 4 except that no nitridation step was conducted. The resultant nitrogen-incorporated silicon oxide film was subjected to a Fourier Transform Infrared (FT-IR) spectrum analysis. FIG. 11 is a Fourier Transform Infrared (FT-IR) spectrum of the nitrogen-incorporated silicon oxide film (“a: Treated”) according to Example 4 and that of the silicon oxide film (“b: Depo only”) according to Comparative Example 3. As shown in FIG. 11, the film without treatment (“b: Depo only”) shows a peak at 1065 cm⁻¹ (Si—O stretching vibration) and a peak at 810 cm⁻¹ (Si—O deformation vibration), indicating that this film was indeed a silicon oxide film. The film with treatment (“a: Treated”) shows wavenumber shifts and broader spectrum, e.g., the peak at 1065 cm⁻¹ (Si—O stretching vibration) is shifted to a lower wavenumber, indicating that new bonds such as Si—N bonds (if this were a SiN film, a peak at 880 cm⁻¹ would have been observed) were formed (partially replacing Si—O bonds), and peaks attributed to Si—O bonds and peaks attributed to the new bonds were superimposed. The above shows that nitrogen was incorporated into the film with treatment.

Example 5 and Comparative Example 4

In Example 5, a nitrogen-incorporated silicon oxide film was formed on a Si substrate (Φ300 mm) by PEALD in the same manner as in Example 4, and the number of cycles (Depo+Nitridation) was 50 in place of 20 in Example 4, and also the resultant film thickness was about 80 nm in place of about 33 nm in Example 4. As Comparative Example 4, a silicon oxide film was deposited on a Si substrate (Φ300 mm) by PEALD under the same conditions as in Example 5 except that no nitridation step was conducted. The resultant nitrogen-incorporated silicon oxide film was subjected to an X-ray photoelectron spectroscopy (XPS) analysis. FIG. 13 is analytical results of X-ray photoelectron spectroscopy (XPS) of the nitrogen-incorporated silicon oxide film (“Treated”) in a depth direction of the film according to Example 5 and those of the silicon oxide film (“Depo only”) in a depth direction of the film according to Comparative Example 4. As shown in FIG. 13, in of the nitrogen-incorporated silicon oxide film (“Treated”), nitrogen was successfully incorporated substantially homogeneously throughout the film and replaced oxygen, i.e., Si—N bonds partially replaced Si—O bonds by substitution reaction (the film contains 10.6 atom % of nitrogen).

Example 6 and Comparative Example 5

In Example 6, a nitrogen-incorporated silicon oxide film was formed on a Si substrate (Φ300 mm) by PEALD in the same manner as in Example 4 except that He was used in place of Ar as the dilution gas in the nitridation treatment, and also the resultant film thickness was about 32 nm in place of about 33 nm in Example 4. As Comparative Example 4, a silicon oxide film was deposited on a Si substrate (Φ300 mm) by PEALD under the same conditions as in Example 6 except that no nitridation step was conducted. The resultant nitrogen-incorporated silicon oxide film was subjected to a Fourier Transform Infrared (FT-IR) spectrum analysis. FIG. 12 is a Fourier Transform Infrared (FT-IR) spectrum of the nitrogen-incorporated silicon oxide film (“a: Treated”) according to Example 6 and that of the silicon oxide film (“b: Depo only”) according to Comparative Example 5. As shown in FIG. 12, similar to FIG. 11, the film without treatment (“b: Depo only”) shows a peak at 1065 cm⁻¹ (Si—O stretching vibration) and a peak at 810 cm⁻¹ (Si—O deformation vibration), indicating that this film was indeed a silicon oxide film. The film with treatment (“a: Treated”) shows wavenumber shifts and broader spectrum, e.g., the peak at 1065 cm⁻¹ (Si—O stretching vibration) is shifted to a lower wavenumber and the peak at 810 cm⁻¹ (Si—O deformation vibration) disappears, indicating that nitrogen was incorporated into the film with treatment.

Example 7 and Comparative Example 6

In Example 7, a nitrogen-incorporated silicon oxide film was formed on a Si substrate (Φ300 mm) by PEALD in the same manner as in Example 6 except that the number of cycles in the deposition cycle was 600 in place of 30 in Example 6 and the number of cycles (Depo+Nitridation) was 1 in place of 20 in Example 6, and also the resultant film thickness was about 35 nm in place of about 33 nm in Example 6. As Comparative Example 6, a silicon oxide film was deposited on a Si substrate (Φ300 mm) by PEALD under the same conditions as in Example 7 except that no nitridation step was conducted. The resultant nitrogen-incorporated silicon oxide film was subjected to a Fourier Transform Infrared (FT-IR) spectrum analysis. FIG. 14 is a Fourier Transform Infrared (FT-IR) spectrum of the nitrogen-incorporated silicon oxide film (“a: Treated”) according to Example 7 and that of the silicon oxide film (“b: Depo only”) according to Comparative Example 6. As shown in FIG. 14, similar to FIG. 11, even though the nitridation treatment was conducted only once after the deposition cycles, the film with treatment (“a: Treated”) shows wavenumber shifts and broader spectrum, e.g., the peak at 1065 cm⁻¹ (Si—O stretching vibration; in this spectrum, the peak was measured at 1062.2 cm⁻¹) is shifted to a lower wavenumber (1060.0 cm⁻¹), indicating that nitrogen was incorporated into the film with treatment.

The films were also subjected to other analyses to determine their properties. The results are shown in Table 3 below.

TABLE 3 (numbers are approximate) Condition Depo only Treatment GPC [A/cycle] 0.60 0.60 1 sigma % 2.0 2.1 RI @ 633 nm 1.458 1.467 WERR [/TOX] 2.74 0.69 Vbd [MV/cm] 13.1 14.9 Leakage current @ 8.8E−09 4.7E−09 8 MV [A/cm2] Stress [MPa] −120 −148 FT-IR peak position 1062.2 1060.0 [cm−1]

As shown in Table 3, even when nitrogen was incorporated in only the top layer (which was converted to a silicon oxynitride layer), the film properties are significantly improved, wherein particularly, wet etch rate (“WERR”) and leakage current were remarkably improved. R.I. and FT-IR peak were slightly changed due to incorporation of nitrogen.

FIG. 15 is a graph showing the relationship between wet etch rate relative to thermal oxide film (“WERR [/TOX]”) and the number of wet etching cycles (“Wet etching cycles [times]”) of the nitrogen-incorporated silicon oxide film (“a: Treated”) according to Example 7 and that of the silicon oxide film (“b: Depo only”) according to Comparative Example 6. As shown in FIG. 15, the uppermost layer of the nitrogen-incorporated silicon oxide film (“Treated”), which was subjected to the first wet etching cycle, exhibited a significantly low wet etch rate of less than 1.0, indicating that nitrogen penetrated the surface and was effectively incorporated in the uppermost layer. However, at the second and third wet etching cycles, the wet etch rate of the film exhibited wet etch rates as high as those of the film without treatment (“Depo only”) because nitrogen penetrated only a surface region and was incorporated in the uppermost layer of the film which was removed by the first wet etching cycle.

According to the technology disclosed herein, a silicon oxynitride layer can be formed at any desired locations, e.g., only on a top surface, only at an interface area (bottom), in a stripe pattern, or substantially homogeneously throughout the film.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We claim:
 1. A method of forming a nitrogen-incorporated silicon or metal oxide film, comprising steps of: (i) depositing by a plasma a silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (ii) nitriding by a plasma the silicon or metal oxide film using a nitriding gas without using any precursor, said plasma having a second plasma density which is higher than the first plasma density.
 2. The method according to claim 1, further comprising, prior to step (i), (ii) nitriding by a plasma a surface of the substrate using a nitriding gas without using any precursor.
 3. The method according to claim 1, wherein in step (i), the silicon or metal oxide film is deposited by plasma-enhanced atomic layer deposition (PEALD).
 4. The method according to claim 3, wherein the oxidizing gas contains both oxygen and nitrogen.
 5. The method according to claim 3, wherein in step (i), the plasma is a capacitively coupled plasma generated by applying RF power to electrodes, wherein a duration of RF power is 2.0 seconds or less in each cycle of PEALD and a power of RF power is 0.28 W per cm² of the substrate surface or less.
 6. The method according to claim 5, wherein in step (ii), the plasma is generated by applying RF power to the electrodes, wherein a power of RF power is 0.42 W per cm² of the substrate surface or higher.
 7. The method according to claim 1, wherein step (i) and step (ii) are conducted in a same reaction space or different reaction spaces to which an inert gas is supplied through steps (i) and (ii).
 8. The method according to claim 7, wherein in step (ii), a flow ratio of the nitriding gas to the inert gas is 1/99 to 50/50.
 9. The method according to claim 3, wherein step (ii) is repeatedly conducted after every one to 100 cycles of PEALD.
 10. The method according to claim 1, wherein the substrate has a recess pattern and the silicon or metal oxide film is conformally deposited on the recess pattern.
 11. The method according to claim 3, wherein in step (i), the plasma is an inductively coupled plasma generated by applying RF power to electrodes or a remote plasma generated in a remote plasma unit.
 12. A method of forming a nitrogen-incorporated silicon or metal oxide film by converting a silicon or metal oxide film to a silicon or metal oxynitride film at a desired location, comprising steps of: (a) designing a layer structure of a nitrogen-incorporated silicon or metal oxide film, which layer structure is composed of a layer A constituted by a silicon or metal oxide film and a layer B constituted by a silicon or metal oxynitride film; (b) according to the design, depositing, for the layer A, by a plasma the silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (c) according to the design, nitriding, for the layer B, by a plasma the silicon or metal oxide film using a nitriding gas without using any precursor in a manner converting the silicon or metal oxide film to the silicon or metal oxynitride film, said plasma having a second plasma density which is higher than the first plasma density.
 13. The method according to claim 12, wherein the nitrogen-incorporated silicon or metal oxide film is constituted by multiple layers of the layer A and multiple layers of the layer B, alternately layered.
 14. The method according to claim 12, wherein a ratio of a total thickness of the layer A to a total thickness of the layer B is 0/100 to 99/1.
 15. A method of forming an oxygen-incorporated silicon or metal nitride film, comprising steps of: (i) depositing by a plasma a silicon or metal nitride film on a substrate using a precursor containing a silicon or metal and a nitriding gas, said plasma having a first plasma density; and (ii) oxidizing by a plasma the silicon or metal nitride film using an oxidizing gas without using any precursor, said plasma having a second plasma density which is lower than the first plasma density.
 16. A method of forming an element X-incorporated silicon or metal oxide film, comprising steps of: (i) depositing by a plasma a silicon or metal oxide film on a substrate using a precursor containing a silicon or metal and an oxidizing gas, said plasma having a first plasma density; and (ii) exciting an element X-containing gas by a plasma and incorporating the element X into the silicon or metal oxide film without using any precursor for deposition, said plasma having a second plasma density which is higher than the first plasma density.
 17. The method according to claim 16, wherein the element X is selected from the group consisting of B, C, Al, P, S, Ga, and As. 